You are wrongly trying to apply involuntary servitude to a situation where it isn't.
In the case described, the person would be still compensated in the same way, doing the same job, if not for some personal problem with something about the type of person the other is and when that characteristic is protected by law.
Legally, enforcement of anti-discrimination laws is not involuntary servitude. Just as forcing a business to comply with other laws, such as health laws or occupational safety laws, which may require additional work for the person that they may rather not do is not involuntary servitude.
If you want to prove otherwise, show where a court in the US has determined that it is involuntary servitude to be forced not to discriminate in the job you do anyway.
Involuntary Servitude legal definition of Involuntary Servitude. Involuntary Servitude synonyms by the Free Online Law Dictionary.
Plus, since the remedy for failing to perform a service for someone in violation of anti-discrimination laws is monetary, then it isn't involuntary servitude. They can opt to pay the person instead (or simply be smart enough to know how to get around the laws, which really aren't that hard).